1. Field of the Invention
The present invention relates to the measurement of active renin enzyme in a biological sample.
2. The Prior Art
Hypertension is a clinical problem of major significance. It is estimated that approximately 23 million Americans have some form of hypertensive condition. Of these, approximately 15% are renal related, that is, dysfunction of the kidney is indicated and manifests itself in an increased renin level in the blood which is indicative of a renal related hypertensive condition. Of these persons having renal related hypertensive conditions a large number are susceptible to surgical correction after further examination has determined the exact cause for the renal involvement.
The production of renin is generally influenced by pathological changes in circulation (renovascular hypertension) and by mineral corticosteroid metabolism (hypertension related to adrenal gland diseases). Measurement of renin activity, therefore, appears to be of great importance for the identification of possible renal related hypertension. It has even been suggested that there is a striking correlation of coronary and cerebrovascular complications with increasing renin activity in essential hypertension.
Renin acts as a proteolytic enzyme of the kidney by releasing angiotensin which has a vasoconstrictive action which results in a higher blood pressure. The early detection of renin level increases related to a blood pressure increase will provide vital prognostic and diagnostic guidelines for evaluating possible surgical treatment especially in renovascular involvement.
There are presently available two types of renin enzyme activity measurement techniques: (1) bioassay, and (2) radioimmunoassay, both of which are based on indirect methods and are only reproducible under certain very controlled conditions and their reliability is, accordingly, suspect.
The bioassay technique for measuring renin activity is based on angiotensin release after serum incubation. The isolated angiotensin from the incubated serum sample is injected into ganglion blocked rats and the resulting elevated blood pressure of the rat is compared with a standard curve which, in turn, is indicative of the renin level of the original sample.
The basic principle of radioimmunoassay utilizes the specific antigen-antibody reaction. This assay uses a known amount of antibody, present as a limiting factor, which is mixed with a sample containing the released Angiotensin I antigen, which is to be determined, and a known amount of radioactive or labeled antigen. The amount of labeled complex formed is an inverse factor of the Angiotensin I antigen concentration in the sample. The concentration of the antigen in an unknown sample is then determined by comparison with a standard curve.
Accordingly, it should be readily apparent that in each of the foregoing prior art techniques the methods are indirect methods and are considerably complex, time-consuming, difficult to standardize and of questionable reliability, particularly as between various research facilities using various different chemical products in their analysis. Accordingly, a rapid, sensitive, reliable, direct reading, and standardized assay technique for renin activity would be of great value in the diagnostic evaluation of hypertensive patients to determine those with possible renal involvement. The present invention offers such a technique for directly determining amount of active renin enzyme in a sample of either plasma or serum.